Generate constants to match the types they're used as

[ian-h-chamberlain]

For a number of "macro constants", the bindings generate them using the c_int type, but they're actually intended for use as another type like u16 or something.

Might make sense for us to just generate this constant as a u16 via bindgen's ParseCallbacks::int_macro, to help prevent conversions.

In fact I wonder if we can't do this for a bunch of other constants and stop using as, maybe I'll file a separate issue for this more broadly

Originally posted by @ian-h-chamberlain in #156 (comment)